1. Field of the Invention
The present invention relates to a display device and a manufacturing method thereof. More particularly, the present invention relates to a display device including a thin film transistor formed on a substrate thereof, and to a manufacturing method for the display device.
2. Description of the Related Art
In an active matrix type display device, a plurality of pixels are arranged in matrix. In addition, gate signal lines are provided so as to be common to the respective pixels arranged in a row direction, and the gate signal lines are selected in an order in which the gate signal lines are provided in a column direction, whereby scanning signals are supplied thereto. Further, at timing at which the gate signal line is selected, a video signal is supplied via a drain signal line common to the respective pixels arranged in the column direction.
For this reason, each pixel includes a thin film transistor provided for feeding the video signal supplied via the drain signal line to a pixel electrode provided on the pixel through the supply of the scanning signal.
Further, a drive circuit for supplying the gate signal line with the scanning signal and supplying the drain signal line with the video signal is provided on the same substrate on which the pixels are formed. The drive circuit is formed of a circuit including a plurality of thin film transistors.
As the thin film transistor included in the drive circuit, there is known a thin film transistor including an n-type thin film transistor and a p-type thin film transistor, in which semiconductor layers of the n-type thin film transistor and the p-type thin film transistor are made of a polycrystalline silicon (low temperature poly-Si) obtained by crystallizing an amorphous silicon. The thin film transistor in which the semiconductor layer is made of the above-mentioned polycrystalline silicon has high field effect mobility, and can drive the drive circuit at high speed.
For example, JP 05-63196 A discloses the thin film transistor as described above.
However, in the case where the n-type thin film transistor and the p-type thin film transistor are each formed of the semiconductor layer made of a polycrystalline silicon, it is necessary to form, between the semiconductor layer made of a polycrystalline silicon and a drain electrode and between the semiconductor layer made of a polycrystalline silicon and a source electrode, an amorphous silicon in which n-type impurities are doped in the case of the n-type thin film transistor, and an amorphous silicon in which p-type impurities are doped in the case of the p-type thin film transistor.
Therefore, the formation of the amorphous silicon in which n-type impurities are doped and the formation of the amorphous silicon in which p-type impurities are doped need to be performed in different mask processes, which leads to an increase in the number of manufacturing steps.